42 



THE ECOLOGICAL RELATIONS OF ROOTS. 



in late summer and in exposed situations. As has already been men- 

 tioned, late-maturing species are not at all abundant. No late- 

 maturing grasses are components of the prairie flora. Flowering 

 begins later and growth continues much longer on north hillsides. 



Soil temperatures on the two exposures differ notably. These data 

 are shown in table 12, which gives the soil temperature at 1 to 5 feet 

 on April 18 and August 15, 1914, on a northeast and southwest slope 

 respectively. 



Table 11. — Average daily evaporation in cubic centimeters on a northeast 

 and a southwest slope respectively. 



Date. 



SW. slope. 



NE. slope. 



Date. 



SW. slope. 



NE. slope. 



1913. 







1913. 







May 



10. . 



12.0 



10.5 



Sept. 



3. . 



33.0 



21.7 



May 



15. . 



9.8 



6.5 



Sept. 



7. . 



32.1 



21.6 



May 



26. . 



13.1 



10.2 



Sept. 



13. . 



33.6 



23.8 



June 



3. . 



15.2 



10.2 



Sept. 



20. . 



46.0 



20.0 



June 



10. . 



13.0 



8.6 



Sept. 



23. . 



21.0 



17.0 



June 



15.. 



14.2 



7.8 



1914. 







June 



25. . 



7.8 



5.4 



May 



15. . 



20.1 



19.0 



July 



3. . 



11.0 



6.7 



May 



21. . 



19.0 



15.1 



July 



8. . 



21.0 



13.5 



May 



30. . 



17.8 



15.6 



July 



13.. 



27.2 



14.0 



June 



7. . 



20.0 



11.2 



July 



18. . 



31.0 



21.8 



June 



15. . 



16.1 



12.5 



July 



25. . 



30.8 



20.3 



June 



22. . 



32.1 



19.0 



July 



29. . 



41.5 



26.4 



June 



29. . 



19.0 



12.8 



Aug. 



4. . 



33.0 



23.8 



July 



6. . 



27.2 



22.5 



Aug. 



10. . 



39.5 



24.5 



July 



13. . 



44.0 



30.5 



Aug. 



16. . 



26.5 



15.8 



July 



20. . 



44.8 



26.0 



Aug. 



20. . 



38.0 



27.2 



Jvily 



27. . 



49.0 



32.0 



Aug. 



25. . 



44.3 



30.0 



Aug. 



3. . 



51.5 



42.6 



Aug. 



31. . 



43.8 



27.5 



Aug. 



10. . 



57.8 



39.1 











Aug. 



15. . 



64.0 



50.1 



Table 12. 



Depth. 



April 18. 



August 15. 



NE. 



SW. 



NE. 



SW. 



1 foot. . . . 



2 feet 



3 feet.... 



4 feet.... 



5 feet 



45.7°F. 



45.1 



45.0 



45.0 



45.0 



50.3°F. 



50.0 



48.2 



47.0 



46.4 



65.0°F. 



61.7 



58.0 



57.2 



54.5 



73.0°F. 



70.0 



66.2 



64.4 



62.6 



The daily midsummer range at a depth of 3 inches on the northeast 

 and southwest slopes was 12° F. and 26° F. respectively. It is probable 

 that these differences in temperature have considerable effect at least 

 on the rate of root development (Cannon, 1918). 



Summarizing briefly the factors of the habitat in which these 

 studies were carried on, we find a region of moderate winter and low 



